ULTRASONIC AND METALLOGRAPHIC STUDY OF THE HEAT-AFFECTED ZONE OF A CARBON STEEL WELDED JOINT UNDER PLASTIC DEFORMATION AND FATIGUE

Failure of an St3sp steel sample under uniaxial tension and fatigue is studied using metallographic and ultrasonic pulse-echo techniques. Samples are cut out from a welded joint, particularly from a parent metal area and an incomplete recrystallization area in the heat-affected zone. The evolution of persistent slip bands in the heat-affected zone and those in the parent metal are subjected to a comparative analysis. A relationship between Poisson’s ratio determined by the ultrasonic method and the mechanical characteristics of the material is established. Methods for estimating the plasticity life under uniaxial tension and the number of cycles before fatigue failure are proposed.